In recent years, in fields relating to graphic decorative printed matter such as vehicle interior device control panels, household electrical appliance labels and designs on tablet device frames and enclosures, demands are increasing for more convenient and low-cost production of printed matter with greater diversity of design and increasingly high definition, having both fine patterns (for example, dot patterns with diameters of about 100 μm, or fine line patterns), and wide-area solid patterns. There is also a demand for higher quality and higher definition of the visibility of printed images that comprise both fine patterns and solid patterns, by improving the sharpness of the image edge sections in solid patterns while also obtaining a satisfactory leveling property.
Moreover, in the fields of black stripe or black matrix printing, as a type of graphics decoration in electric or electronic fields, there is a demand for obtaining a high degree of definition that provides sharpness to the printed images without bleeding or spreading, in addition to stable printing of fine lines, and there is a desire to be able to accomplish high definition printing with satisfactory visibility in a single step regardless of the size of the printed area, for cost reduction.
In addition, glass substrates are becoming widely used as printed objects in these fields, and various types of glass substrates have come into use for glass substrates, including untreated glass, antifog-treated glass, tempered glass, anti-reflection-treated glass, thermal ray blocking-treated glass, colored glass and ITO conductive film-treated glass, while the printing surface conditions of glass substrates (such as the wetting index) are also becoming diversified. Still, a strong demand exists for a high-quality/high-definition screen printing ink for glass substrates that can be used for glass substrates having such a variety of surface conditions, while retaining satisfactory adhesion and durability, and having stable printing properties for fine lines, as well as a high degree of sharp high definition without bleeding or spreading in printed images, and also allowing high definition printing with satisfactory visibility in a single step regardless of the size of the printed area.
In conventional screen printing, when printing a dot pattern or fine line pattern of approximately 100 μm, printing is usually performed using a high-viscosity screen printing ink of about 10 to 200 Pa·s, with a reduced flow property, but printing of solid patterns with such high-viscosity screen printing inks cannot avoid creation of leveling defects or printing abnormalities in the solid patterns due to the poor flow property, and as a result the visibility of the printed matter is impaired. Furthermore, when a low-viscosity screen printing ink of several Pa·s is used for satisfactory printing of solid patterns, it has been impossible to avoid spreading of ink that may exceed about 50 to 100 μm at the solid pattern image edge sections, or enlargement, spreading or bleeding of fine patterns, that impair the visibility of the printed matter, and therefore screen printing of fine patterns and solid patterns is performed separately with different inks suitably prepared for each, and it has been difficult to produce printed matter comprising both fine patterns and solid patterns in a single step of screen printing.
Ink jet printing, on the other hand, is considered to allow high-precision printing of printed matter comprising both fine patterns and solid patterns in a single step, and many attempts have been made to accomplish high-quality/high-definition printing by ink jet printing, however, since ink jet printing involves spraying ink droplets from a head nozzle with a diameter of about 30 μm, which spread out to about 50 μm at minimum when the droplets impact with the object being printed, it has been the case that such printing lacks sharp linearity especially at image edge sections.
Offset printing is another printing system that allows creation of high-quality/high-definition printed matter, however, since the structure of the printing plate is mesh-like, resulting in the printed images that are aggregated prints of halftone dots, it has been impossible to avoid a lack of sharp linearity at image edge sections, similar to ink jet printing, while the printing film thickness is also thin at about 1 to 2 μm, and when compared to screen printed matter, it is inferior in terms of high film thickness, high durability, high weather resistance and high chemical resistance, as well as firm adhesion to various objects to be printed and versatile functionality, such that it is unsuitable for creation of printed matter that requires durability and functionality, such as vehicle interior device control panels and household electrical appliance labels, designs on tablet device frames and enclosures, and light modulated black stripes and black matrices.
Prior Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2010-047716) and Prior Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2010-047649) each disclose a conductive ink composition and conductive coating film for screen printing that can form high-definition patterns, but techniques relating to the flow property of ink for printing with both fine patterns and solid patterns have not been pursued, and therefore while fine patterns can be obtained with satisfactory printing precision, in the case of solid patterns, the leveling property is poor and printing abnormalities are generated. Furthermore, the technical scope of Prior Patent Document 1 relates only to printing of fine patterns with the conductive ink composition. Moreover, they do not disclose any technique relating to a screen ink composition printed with high precision onto various different types of glass substrates.
In addition, Prior Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2003-238876) and Prior Patent Document 4 (Japanese Unexamined Patent Application Publication No. 2003-294930) disclose ink compositions for screen printing that allow formation of high-definition patterns, but as with Prior Patent Document 1, the disclosures are of techniques for highly precise printing of fine patterns but not of technology relating to ink compositions for simultaneous printing of solid patterns in a single step. Moreover, they do not disclose any technique relating to a screen ink composition printed with high precision onto various different types of glass substrates.